The following passage describes the need and evolution of the subject technology in the field of thin film batteries.
Thin-film batteries may be fabricated by sequential vacuum depositions of layered battery components onto a given substrate in, for example, the following order: positive cathode current collector, positive cathode, negative anode current collector, electrolyte (separator), negative anode, and encapsulation. A lamination process may be used instead of a deposition process step (see, for example, U.S. Pat. No. 6,916,679 versus Wang et al., 143 J. Electrochem. Soc. 3203-13 (1996) or U.S. Pat. No. 5,561,004). Optionally, the two terminals of a thin-film battery may not simply comprise extensions of the positive and the negative current collectors, but may be additionally deposited terminal contacts that make electrical contact to the respective current collector. The positive cathode material may be insufficiently crystalline in the as-deposited state and, associated with this fact, may exhibit insufficient electrochemical properties (see, for example, Wang et al., supra). For this reason, the positive cathode may be crystallized during battery fabrication, which can be achieved in a post-deposition, high-temperature (“anneal”) process (see, for example, Wang et al., supra or Bates et al., “Thin-Film Lithium Batteries” in New Trends in Electrochemical Technology: Energy Storage Systems for Electronics (T. Osaka & M. Datta eds., Gordon and Breach 2000)). The anneal process, which is applied immediately after the deposition of the positive cathode, may limit the choice of materials for the substrate and positive cathode current collector, thereby limiting, in turn, the capacity density, energy density, and power density of the thin-film battery, both per volume and weight. The affect of the substrate on those three quantities is, for example, explained in more detail below.
The intrinsic (i.e., without substrate and without encapsulation) volumetric and gravimetric densities of the capacity, the energy, and the power of lithium-based, solid-state, thin-film secondary (rechargeable) and primary (non-rechargeable) batteries are dominated by the volumetric and gravimetric densities of the capacity, the energy, and the power of the positive cathode material. Crystalline LiCoO2 may be an example of a choice for the positive cathode material for both bulk (non thin-film) and thin-film batteries in terms of volumetric and gravimetric densities of the capacity, energy, power, and cyclability, in the case of secondary batteries, followed by derivatives of crystalline LiMn2O4, crystalline LiMnO2, and crystalline LiNiO2. Doping these main parent positive cathode materials with other transition metals (leading to derivatives) such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, La, Hf, Ta, W, and Re and main group elements selected from the groups 1, 2, 13, 14, 15, 16 and 17 has been found to alter the properties of LiCoO2, LiMn2O4, LiMnO2, and LiNiO2 with only little, if any, overall improvement.
According to U.S. Pat. No. 6,280,875, native titanium oxide on a Ti substrate is not inert enough to prevent adverse reactions from occurring between a Ti substrate and the battery components. This approach is severely restricted because the choice of substrate materials is limited to materials capable of forming a native surface oxide during the anneal step of the positive cathode. Apart from the present invention, metallic substrates including flexible foils that do not form a native surface oxide have not been employed successfully as thin-film battery substrates. Fabricating solid-state, thin-film secondary batteries by depositing, for example, high-temperature cathode materials directly onto metallic substrates, including flexible foils, other than Zr, and then annealing at high temperature, such as 700° C. in air for 1 hour, may result in the positive cathode and substrate materials reacting detrimentally to such an extent that the positive cathode is rendered useless. Pure Ti and Zr substrates are also relatively expensive.
Prior thin-film batteries do not disclose the use of an effective barrier layer between the substrate and the battery, and, therefore, provide potential negative observations. A need exists for the present invention such as, for example, an inventive barrier layer with sublayering attributes to overcome certain problems of prior thin film-batteries.